Transmitter, receiver, transmitting method, and receiving method

ABSTRACT

A transmitter includes a mapping circuit and a framing circuit. The mapping circuit is configured to combine and map a first data sequence and a second data sequence onto orthogonal frequency division multiplexing (OFDM) subcarriers which include first subcarriers and second subcarriers. The framing circuit is configured to generate an OFDM signal from the OFDM subcarriers. The mapping circuit is configured to: map first data included in the first data sequence and second data included in the second data sequence onto the first subcarriers; and map the second data onto the second subcarriers. The first data are not mapped on the second subcarriers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/EP2017/076397 filed on Oct. 17, 2017,claiming the benefit of priority of European Patent Application Number16195317.9 filed on Oct. 24, 2016 and European Patent Application Number17164111.1 filed on Mar. 31, 2017, the entire contents of which arehereby incorporated by reference.

1. TECHNICAL FIELD

The present disclosure relates to a transmitter, a receiver, atransmitting method, and a receiving method.

2. DESCRIPTION OF THE RELATED ART

Multiplexing multiple signals into a compound signal is a common methodin data communications to share a single medium. Traditionally, datacarrying different services are multiplexed in time or frequency. Thesemethods are called Time-Division-Multiplex (TDM) andFrequency-Division-Multiplex (FDM). Real-world applications for TDM andFDM can be found in DVB-T2, in which multiple so-called PLPs (PhysicalLayer Pipes), each characterized by their own modulation and timeinterleaver, are sharing a certain frequency band in dedicated timeslots, and the Japanese ISDB-T standard with the prominent One-Segsystem, in which data is carried in banded segments which are strictlyseparated in frequency domain thus allowing for power-saving partialreception of individual segments.

It has been long since known that FDM and TDM are not the most efficientmethods to share a medium. Their benefit lays more with the ease ofimplementation. From “Cooperative broadcasting” by P. P. Bergmans and T.M. Cover, IEEE Trans. Inf. Theory, vol. 20, no. 3, pp. 317-324, May 1974(non-patent literature (NPL) 1), for instance, it is known that thesuperposition of different services increases the capacity over eitherTDM or FDM. Only recently, this form of multiplexing has found its wayinto a current standard, namely ATSC 3.0, where it is calledLayered-Division-Multiplexing (LDM); cf. “Low Complexity LayeredDivision for ATSC 3.0,” by S. I. Park, et. al., IEEE Transactions onBroadcasting, vol. 62, no. 1, pp. 233-243, March 2016 (NPL 2).

Intuitively, the edge of LDM over TDM/FDM in capacity is obtained due tothe simultaneous transmission of more than one service without pausingin either time domain or frequency domain. In practice, however, LDMentails higher receiver complexity as well as constraints in thetransmission system design.

SUMMARY

According to an aspect of the present disclosure, a transmitter includesa mapping circuit and a framing circuit. The mapping circuit isconfigured to combine and map a first data sequence and a second datasequence onto orthogonal frequency division multiplexing (OFDM)subcarriers which include first subcarriers and second subcarriers. Theframing circuit is configured to generate an OFDM signal from the OFDMsubcarriers. The mapping circuit is configured to: map first dataincluded in the first data sequence and second data included in thesecond data sequence onto the first subcarriers; and map the second dataonto the second subcarriers. The first data are not mapped on the secondsubcarriers.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram which illustrates a conventional technique forconstellation superposition for two-layer LDM according to ATSC 3.0;

FIG. 2A is a spectrum diagram which illustrates strictly orthogonalsubcarriers as received over a static channel;

FIG. 2B is a spectrum diagram which illustratesintercarrier-interference among subcarriers received over a rapidlytime-varying channel;

FIG. 3 is a spectrum diagram which illustrates reducedintercarrier-interferences in a situation where only every othersubcarrier is modulated;

FIG. 4A is a spectrum diagram which illustrates subcarriers in asituation where LDM and OFDM are used on a static channel;

FIG. 4B is a spectrum diagram which illustrates subcarriers in asituation where LDM and OFDM are used on a rapidly time varying channel;

FIG. 5 is a block diagram which illustrates a technique forconstellation superposition for two-layer LDM according to Embodiment 1;

FIG. 6A is a spectrum diagram which illustrates transmitted OFDM symbolswith an LDM compound signal according to Embodiment 1;

FIG. 6B is a spectrum diagram which illustrates OFDM symbols with an LDMcompound signal received over a rapidly time-varying channel, accordingto Embodiment 1;

FIG. 7 is a schematic block diagram of a transmitter for two LDM layersaccording to Embodiment 1;

FIG. 8A is a schematic block diagram of a receiver for the upper layeraccording to Embodiment 1;

FIG. 8B is a schematic block diagram of a SIC-Receiver for the lowerlayer according to Embodiment 1;

FIG. 9 is a block diagram which illustrates a technique forconstellation superposition and interleaving for two-layer LDM accordingto Embodiment 2;

FIG. 10A is a spectrum diagram which illustrates transmitted OFDMsymbols with an LDM compound signal according to Embodiment 2;

FIG. 10B is a spectrum diagram which illustrates OFDM symbols with anLDM compound signal received over a rapidly time-varying channel,according to Embodiment 2;

FIG. 11A is a schematic representation of a sequence of LDM compoundcells output by an LDM combiner with upper-layer up-sampling and M=3;

FIG. 11B is a schematic representation of the interleaving stageoperating on the cell sequence of FIG. 11A;

FIG. 12A is a schematic illustration of one core PLP and one enhancedPLP from a single LDM-group;

FIG. 12B is a schematic illustration of one core PLP and one enhancedPLP in a first LDM-group 0, and a single PLP in a second LDM-group 1;

FIG. 12C is a schematic illustration of three PLPs on the core layer anda single PLP on the enhanced layer, which yield three LDM-groups;

FIG. 12D is a schematic illustration of a single PLP on the core layerand three PLPs on the enhanced layer, which yield a single LDM-group;

FIG. 12E is a schematic illustration of two PLPs on core and enhancedlayer, which yield two LDM-groups, with the fourth PLP (plp_id_3) beingshared by two LDM-groups;

FIG. 13A is a schematic illustration of a time interleaver layout forthe upper layer.

FIG. 13B is a schematic illustration of a time interleaver layout forthe lower layer and a single PLP on the lower layer;

FIG. 14A is a schematic illustration of one of two enhanced PLPs whichare passed through the lower layer time-interleaver;

FIG. 14B is a schematic illustration of the other of two enhanced PLPswhich are passed through the lower layer time-interleaver;

FIG. 14C is a schematic illustration of the lower layertime-interleaver;

FIG. 15 is a schematic illustration of applying the frequencyinterleaver in chunks of Ndata cells to the time-interleaver output ofin total K cells;

FIG. 16A is a schematic block diagram of a receiver for the upper layeraccording to Embodiment 2;

FIG. 16B is a schematic block diagram of a SIC-Receiver for the lowerlayer according to Embodiment 2;

FIG. 17 is a block diagram of a configuration of the transmitteraccording to the respective embodiments;

FIG. 18 is a block diagram of a configuration of the receiver accordingto the respective embodiments;

FIG. 19 is a flowchart illustrating the transmitting method according tothe respective embodiments; and

FIG. 20 is a flowchart illustrating the receiving method according tothe respective embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A transmitter according to an aspect of the present disclosure is atransmitter that transmits a first data sequence and a second datasequence by orthogonal frequency division multiplexing (OFDM), thetransmitter including: a mapper that obtains the first data sequence andthe second data sequence, and combines and maps the first data sequenceand the second data sequence obtained onto a plurality of subcarrierswhich are OFDM subcarriers; and a framer that generates an OFDM signalfrom the plurality of subcarriers, wherein the mapper: (a) maps dataincluded in the first data sequence and data included in the second datasequence onto a plurality of first subcarriers out of the plurality ofsubcarriers; and (b) maps the data included in the second data sequence,out of the data included in the first data sequence and the dataincluded in the second data sequence, onto a plurality of secondsubcarriers different from the plurality of first subcarriers, out ofthe plurality of subcarriers.

According to the above-described aspect, the transmitter is capable ofappropriately mapping and transmitting a first data sequence and asecond sequence on OFDM subcarriers. Specifically, the first subcarriersinclude the data included in the first data sequence and the dataincluded in the second data sequence, and second subcarriers includeonly the data included in the second data sequence, out of the dataincluded in the first data sequence and the data included in the seconddata sequence. Therefore, the data included in the first data sequenceare placed in the subcarriers at wider intervals along the frequencyaxis than the data included in the second data sequence. As such, thereis the advantage that, even if the frequency width of the subcarrierwidens due to the effects of a Doppler shift, etc., duringcommunication, the data included in the first data sequence is moreresilient to the effects of such widening than the second data sequence.Furthermore, the data included in the second data sequence are placed inthe subcarriers at narrower intervals along the frequency axis than thedata included in the first data sequence. As such, there is theadvantage that the data included in the second data sequence is allowedto be data of bigger volume than the data included in the first datasequence. In this manner, the error-resilience of the data included inthe first data sequence can be improved and the allowable data volumefor the data included in the second data sequence can be increased. Inthis manner, the transmitter according to the present disclosure iscapable of improving digital data transmission performance.

For example, the mapper may map the data by using the plurality of firstsubcarriers, the plurality of first subcarriers being every n-thsubcarrier along a frequency axis, n being a predetermined integer.

According to the above-described aspect, the transmitter maps both thedata included in the first data sequence and the data included in thesecond data sequence onto every n-th subcarrier along a frequency axis,n being a predetermined integer. Accordingly, since the subcarriers ontowhich the data included in the first data sequence have uniformintervals along the frequency axis, it is possible to further improveresilience against the effects of a Doppler shift, etc., duringcommunication.

For example, the mapper may: (a) map the data included in the first datasequence onto the plurality of first subcarriers, as a high powersignal; and (b) map the data included in the second data sequence ontothe plurality of first subcarriers and the plurality of secondsubcarriers, as a low power signal having power lower than power of thehigh power signal, and a ratio of the power of the high power signal tothe power of the low power signal may be bigger when the predeterminedinteger is bigger.

According to the above-described aspect, the transmitter can make thetransmission power approximately uniform by increasing the power of thesignal of the data included in the first data sequence according to theinterval along the frequency axis.

For example, the transmitter may further include an interleaver thatinterleaves the data mapped onto the plurality of subcarriers, whereinthe framer may generate the OFDM signal from the plurality ofsubcarriers after the interleaving by the interleaver, and theinterleaver may: (a) switch the data mapped onto one first subcarrierwith the data mapped onto another first subcarrier, the one firstsubcarrier and the other first subcarrier being included in theplurality of first subcarriers; and (b) switch the data mapped onto onesecond subcarrier with the data mapped onto another second subcarrier,the one second subcarrier and the other second subcarrier being includedin the plurality of second subcarriers.

According to the above-described aspect, the transmitter performs theinterleaving of data mapped onto the first subcarriers and theinterleaving of data mapped onto the second subcarriers. Accordingly,interleaving of transmission data (i.e., data to be transmitted) can beperformed while suppressing transmission power fluctuation.

For example, the interleaver may include a frequency interleaver, andthe frequency interleaver may: (a) switch the data mapped onto the onefirst subcarrier with the data mapped onto the other first subcarrier,the other first subcarrier being different in frequency from the onefirst subcarrier; and (b) switch the data mapped onto the one secondsubcarrier with the data mapped onto the other second subcarrier, theother second subcarrier being different in frequency from the one secondsubcarrier.

According to the above-described aspect, the transmitter uses frequencyinterleaving for the interleaving. The transmitter performs interleavingof transmission data based on a specific configuration such as thatdescribed above.

For example, the interleaver may include a time interleaver, and thetime interleaver may: (a) switch the data mapped onto the one firstsubcarrier with the data mapped onto the other first subcarrier, theother first subcarrier being different from the one first subcarrier inat least one of frequency and time; and (b) switch the data mapped ontothe one second subcarrier with the data mapped onto the other secondsubcarrier, the other second subcarrier being different from the onesecond subcarrier in at least one of frequency and time.

According to the above-described aspect, the transmitter uses timeinterleaving for the interleaving. The transmitter performs interleavingof transmission data based on a specific configuration such as thatdescribed above.

A receiver according to an aspect of the present disclosure is areceiver that receives a first data sequence and a second data sequenceby orthogonal frequency division multiplexing (OFDM), the receiverincluding: a receiving device that receives an OFDM signal; and aretriever that retrieves the first data sequence and the second datasequence from the OFDM signal received by the receiving device, whereinthe retriever: (a) retrieves data included in the first data sequenceand data included in the second data sequence, from a plurality of firstsubcarriers out of a plurality of subcarriers which are OFDMsubcarriers; and (b) retrieves the data included in the second datasequence out of the data included in the first data sequence and thedata included in the second data sequence, from a plurality of secondsubcarriers different from the first subcarriers, out of the pluralityof subcarriers.

According to the above-described aspect, the receiver is capable ofreceiving the OFDM subcarriers onto which the first data sequence andthe second sequence have been appropriately mapped. Specifically, thefirst subcarriers include the data included in the first data sequenceand the data included in the second data sequence, and secondsubcarriers include only the data included in the second data sequence,out of the data included in the first data sequence and the dataincluded in the second data sequence. Therefore, the data included inthe first data sequence are placed in the subcarriers at largerintervals in the frequency axis than the data included in the seconddata sequence. As such, there is the advantage that, even if thefrequency width of the subcarrier widens due to the effect of a Dopplershift, etc., during communication, the data included in the first datasequence is not as affected by the widening as the second data sequence.Furthermore, the data included in the second data sequence are placed inthe subcarriers at narrower intervals along the frequency axis than thedata included in the first data sequence. As such, there is theadvantage that the data included in the second data sequence can be dataof bigger volume than the data included in the first data sequence. Inthis manner, the error-resilience of the data included in the first datasequence can be improved and the allowable data volume for the dataincluded in the second data sequence can be increased. In this manner,the receiver according to the present disclosure is capable of improvingdigital data receiving performance.

For example, the retriever may retrieve the data by using the pluralityof first subcarriers, the plurality of first subcarriers being everyn-th subcarrier along a frequency axis, n being a predetermined integer.

According to the above-described aspect, the receiver is able to receiveboth the data included in the first data sequence and the data includedin the second data sequence that have been mapped onto every n-thsubcarrier along the frequency axis, n being a predetermined integer.

Accordingly, since the subcarriers onto which the data included in thefirst data sequence have uniform intervals along the frequency axis, itis possible to further improve resilience against the effects of aDoppler shift, etc., during communication.

For example, the retriever may: (a) retrieve the data included in thefirst data sequence from the plurality of first subcarriers, as a highpower signal; and (b) retrieve the data included in the second datasequence from the plurality of first subcarriers and the plurality ofsecond subcarriers, as a low power signal having power lower than powerof the high power signal, and a ratio of the power of the high powersignal to the power of the low power signal may be bigger when thepredetermined integer is bigger.

According to the above-described aspect, the receiver can make thereceiving power approximately uniform by increasing the power of thesignal included in the first data sequence according to the intervalalong the frequency axis.

For example, the receiver may further include a deinterleaver thatdeinterleaves the data mapped onto the plurality of subcarriers byswitching the data mapped onto one first subcarrier with the data mappedonto another first subcarrier and switching the data mapped onto onesecond subcarrier with the data mapped onto another second subcarrier,in the OFDM signal received by the receiving device, the one firstsubcarrier and the other first subcarrier being included in theplurality of first subcarriers, the one second subcarrier and the othersecond subcarrier being included in the plurality of second subcarriers.

According to the above-described aspect, the receiver performs thedeinterleaving of data mapped onto the first subcarriers and thedeinterleaving of data mapped onto the second subcarriers. Accordingly,deinterleaving of received data can be performed while suppressingreceiving power fluctuation.

For example, the deinterleaver may include a frequency deinterleaver,and the frequency deinterleaver may: (a) switch the data mapped onto theone first subcarrier with the data mapped onto the other firstsubcarrier, the other first subcarrier being different in frequency fromthe one first subcarrier; and (b) switch the data mapped onto the onesecond subcarrier with the data mapped onto the other second subcarrier,the other second subcarrier being different in frequency from the onesecond subcarrier.

According to the above-described aspect, the receiver uses frequencydeinterleaving for the deinterleaving. The receiver performsdeinterleaving of received data based on a specific configuration suchas that described above.

For example, the deinterleaver may include a time deinterleaver, and thetime deinterleaver may: (a) switch the data mapped onto the one firstsubcarrier with the data mapped onto the other first subcarrier, theother first subcarrier being different from the one first subcarrier inat least one of frequency and time; and (b) switch the data mapped ontothe one second subcarrier with the data mapped onto the other secondsubcarrier, the other second subcarrier being different from the onesecond subcarrier in at least one of frequency and time.

According to the above-described aspect, the receiver uses timedeinterleaving for the deinterleaving. The receiver performsdeinterleaving of received data based on a specific configuration suchas that described above.

A transmitting method according to an aspect of the present disclosureis a transmitting method of transmitting a first data sequence and asecond data sequence by orthogonal frequency division multiplexing(OFDM), the transmitting method including: obtaining the first datasequence and the second data sequence, and combining and mapping thefirst data sequence and the second data sequence obtained onto aplurality of subcarriers which are OFDM subcarriers; and generating anOFDM signal from the plurality of subcarriers, wherein in the mapping:(a) data included in the first data sequence and data included in thesecond data sequence are mapped onto a plurality of first subcarriersout of the plurality of subcarriers; and (b) the data included in thesecond data sequence, out of the data included in the first datasequence and the data included in the second data sequence, are mappedonto a plurality of second subcarriers different from the plurality offirst subcarriers, out of the plurality of subcarriers.

Accordingly, the same advantageous effects as with the above-describedtransmitter are produced.

A receiving method according to an aspect of the present disclosure is areceiving method of receiving a first data sequence and a second datasequence by orthogonal frequency division multiplexing (OFDM), thereceiving method including: receiving an OFDM signal; and retrieving thefirst data sequence and the second data sequence from the OFDM signalthat was received, wherein in the retrieving: (a) data included in thefirst data sequence and data included in the second data sequence areretrieved from a plurality of first subcarriers out of a plurality ofsubcarriers which are OFDM carriers; and (b) the data included in thesecond data sequence, out of the data included in the first datasequence and the data included in the second data sequence, areretrieved from a plurality of second subcarriers different from thefirst subcarriers, out of a plurality of subcarriers.

Accordingly, the same advantageous effects as with the above-describedreceiver are produced.

It should be noted that these general and specific aspects may beimplemented using a system, an apparatus, an integrated circuit, acomputer program, or a computer-readable recording medium such as aCD-ROM, or any combination of systems, apparatuses, integrated circuits,computer programs, or recording media.

Hereinafter, embodiments will be specifically described with referenceto the Drawings.

Furthermore, each of the embodiments described below shows a generic orspecific example. The numerical values, shapes, materials, structuralcomponents, the arrangement and connection of the structural components,steps, the processing order of the steps etc. shown in the followingembodiments are mere examples, and are therefore not intended to limitthe present disclosure. Furthermore, among the structural components inthe following embodiments, structural components not recited in any oneof the independent claims defining the most generic concepts aredescribed as arbitrary structural components.

Embodiment 1

According to a first aspect of the present disclosure, a method fortransmitting digital data is provided. The method comprises the steps ofgenerating a first modulated signal by modulating digital data of afirst service; generating a second modulated signal by modulatingdigital data of a second service; generating a compound signal by addingthe first modulated signal and the second modulated signal; andtransmitting the compound signal. The method is characterized byup-sampling the first modulated signal by a factor of M, M being apositive integer greater than 1, wherein the compound signal isgenerated by adding the up-sampled signal and the second modulatedsignal.

The first modulated signal is, for example, up-sampled by inserting(M−1) zeroes between every two consecutive samples of the firstmodulated signal. Other up-sampling methods are conceivable, butsuppression of inter-carrier interference is most effective if spectralenergy of sub-carriers not carrying the first service is reduced tozero.

In an exemplary embodiment, the up-sampled signal may be scaled by afactor of sqrt(M) in order to compensate the reduction of power causedby the up-sampling process. Different scaling factors that approximatethe theoretical value of sqrt(M) may also be used. Other embodiments maydispense with the compensation of power reduction.

In another exemplary embodiment, the second modulated signal is scaledby a predefined positive factor smaller than or equal to 1 in order tocontrol the injection level of the second layer data. This step can bedispensed with if the modulation of the second layer data results in amodulated signal with the appropriate amplitude. Additionally oralternatively, a power level of the compound signal may be normalized byanother scaling operation. Other means for controlling the injectionlevel and the overall power of the compound signal are conceivable,including scaling both the first modulated signal and the secondmodulated signal by appropriate weights prior to the adding step.

An exemplary embodiment further comprises the step of dividing thecompound signal into frames of a predefined length, wherein data of eachframe is transmitted simultaneously by means of orthogonal frequencydivision multiplexing, OFDM.

OFDM is the preferred method for transmitting digital data over abroadband communication channel and is used in many digital broadcastingand communication standards, including DVB-T2 and ATSC 3.0.

For example, data of the first service is transmitted on every M-th OFDMsubcarrier only. This reduces ICI for the first layer data ontime-varying channels and allows at the same time long OFDM symbols forthe second layer data. Mobile devices may thus receive the first servicewith high reliability, whereas stationary devices may additionallyreceive the second service at a high data rate.

According to a second aspect of the present disclosure, a method forreceiving digital data is provided. Said method comprises the steps ofreceiving a compound signal; down-sampling the received compound signalby a factor of M, M being a positive integer greater than 1; andretrieving digital data of a first service by demodulating thedown-sampled signal.

In an exemplary embodiment, the method further comprises the steps ofgenerating a re-modulated signal by modulating the retrieved digitaldata of the first service; up-sampling the re-modulated signal by thefactor of M; generating a difference signal by subtracting theup-sampled signal from the compound signal; and retrieving digital dataof a second service by demodulating the difference signal.

The receiving method may further comprise the step of scaling theup-sampled and re-modulated signal by a factor of sqrt(M), in order tocompensate the power reduction caused by the up-sampling process.

In an exemplary embodiment, the compound signal is received by decodinga sequence of OFDM symbols. Moreover, the down-sampling step may keepevery M-th OFDM subcarrier only, thereby achieving the advantages of thepresent disclosure, i.e., a reduction of ICI on rapidly time-varyingchannels.

According to a third aspect of the present disclosure, a transmitter fortransmitting digital data is provided. The transmitter comprises a firstmodulator for generating a first modulated signal by modulating digitaldata of a first service; a second modulator for generating a secondmodulated signal by modulating digital data of a second service; asignal combiner for generating a compound signal by adding the firstmodulated signal and the second modulated signal; and an output stagefor transmitting the compound signal. The transmitter is characterizedby an up-sampling unit for up-sampling the first modulated signal by afactor of M, M being a positive integer greater than 1, wherein thecompound signal is generated by adding the up-sampled signal and thesecond modulated signal.

According to a fourth aspect of the present disclosure, a receiver forreceiving digital data is provided. The receiver comprises an inputstage for receiving a compound signal; a down-sampling unit fordown-sampling the received compound signal by a factor of M, M being apositive integer greater than 1; a first demodulator for retrievingdigital data of a first service by demodulating the down-sampled signal.

In an exemplary embodiment, the receiver further comprises a modulatorfor generating a re-modulated signal by modulating the retrieved digitaldata of the first service; an up-sampling unit for up-sampling there-modulated signal by the factor of M; a signal subtractor forgenerating a difference signal by subtracting the up-sampled signal fromthe compound signal; and a second demodulator for retrieving digitaldata of a second service by demodulating the difference signal. In thismanner the receiver is capable of retrieving both the first layer dataand the second layer data.

Hereinafter, Embodiment 1 will be described in detail.

FIG. 1 illustrates the general concept of LDM for two layers, which arecalled upper and lower layer. In principle, of course, more than twolayers are conceivable. Both layers can carry one or more physical layerpipes (PLPs). The upper layer carries a low-rate service x_(U) aimed atmobile reception, while the lower layer carries a high-rate servicex_(L) aimed at stationary reception. An injection level controllerprovides a scaling factor α≤1 which lowers the power of the lower layer,followed by a superposition of the two layers yielding thenon-normalized signal x_(U)+α x_(L). The compound signal is subsequentlynormalized to unit power via an appropriate scaling factor β.

It should be noted that a data sequence carried by the upper layer isalso referred to as a first data sequence, and the data sequence carriedby the lower layer is also referred to as a second data sequence.

ATSC 3.0, a new digital terrestrial television (DTT) system and thefirst to implement LDM, is based on orthogonal frequency divisionmultiplexing (OFDM) and bit-interleaved coded modulation (BICM). In FIG.1, there is thus a first BICM unit (10) for the digital data of theupper layer and a second BICM unit (20) for the digital data of thelower layer. Each BICM unit (10, 20) includes an encoder (not shown) forencoding the input data with an error correcting code, a bit interleaver(not shown) for increasing the resilience to burst errors, and a symbolmapper (not shown) for mapping the coded and interleaved bit sequenceinto a base-band sequence of complex digital symbols or cells. Here, thesequence of symbols is also referred to as a modulated signal.

The modulated signal of the lower layer is fed through the injectionlevel controller (30), which applies a scaling by factor α≤1. The scaledlower layer signal and the (unscaled) upper layer signal are thencombined by means of a signal adder (40), which performs algebraicaddition on a cell-by-cell basis. The result of this operation may bescaled once more in order to normalize the power of the compound signal(power normalization unit 50). The process of controlling the injectionlevel and the process of normalizing the power of the compound signalmay also be combined into a single step of computing a suitably weightedsum of the two signals, or performed in any other suitable manner.

It is noted that in ATSC 3.0, the upper layer is called core layer, andthe lower layer enhanced layer. Other than that layered divisionmultiplexing was specified as depicted in FIG. 1.

The corresponding receiver operation is understood such that a mobilereceiver, which is interested in the upper layer only, also detects theupper layer only. A stationary receiver interested in the lower layer isrequired to perform successive interference cancellation, i.e., theupper layer is detected first. Assuming that the upper layer is detectedsuccessfully, it is then re-modulated and the re-modulated cells aresubtracted from the received cells in order to detect eventually thelower layer.

According to FIG. 1, each cell of the upper layer is paired with acorresponding cell from the lower layer resulting in a compound signalwhich is subsequently passed on to the interleaving stages, the framingand finally OFDM itself.

Here, the first compromise can be observed: time interleaving andfrequency interleaving are applied to the compound signal, althoughdifferent interleaving stages might be desirable for mobile andstationary signals. It is conceivable that both signals employ dedicatedinterleaving stages; this leads, however, to increased receivercomplexity on account of additional interleaving operations during thesuccessive interference cancellation.

The second compromise follows from the carriage of the compound signalon a single OFDM signal, i.e., both layers implicitly use the same FFTlength. Here, a clear design conflict comes to light: the mobile upperlayer would benefit from a short FFT to be resilient against Dopplerspread, while the stationary lower layer would benefit from a long FFTto minimize the loss in terms of the guard interval. In practice, amiddle ground is chosen in the form of an 8 k or 16 k FFT rather than a32 k FFT.

Orthogonal Frequency Division Multiplexing is an established method totransmit data over a wide bandwidth. Multipath effects are elegantlycoped with by transmitting data in orthogonal subcarriers, and byadditionally expanding the OFDM symbol duration beyond the maximumexpected delay spread of the channel using a cyclic prefix whichsimplifies the equalization step at the receiver.

FIG. 2A is a spectrum diagram which illustrates strictly orthogonalsubcarriers as received over a static channel. The subcarrier spectraexhibit their typical sinc-type behavior and at integer multiples of thenormalized frequency f T_(S) only a single subcarrier is non-zero, whileall neighboring subcarriers are passing through zero. Here, f T_(S)denotes the frequency f normalized to the subcarrier spacing 1/T_(S)with T_(S) denoting the OFDM symbol duration.

However, the prolonged symbol duration makes OFDM vulnerable totime-varying changes of the channel. In particular, the orthogonality ofthe subcarriers is lost if the channel impulse response changes duringan OFDM symbol. This is a straightforward consequence of the Fouriertransformation and its correspondences between time and frequencydomain. As a consequence of the lost subcarrier orthogonality infrequency domain after the FFT, intercarrier-interference (ICI) mayoccur, which diminishes the carrier-to-interference-and-noise-power CINRand the more so the faster the receiver is moving.

FIG. 2B is a spectrum diagram which illustratesintercarrier-interference among subcarriers received over a rapidlytime-varying channel. As can be seen, the subcarrier spectra are widenedon account of a time-varying channel and thus at any given subcarriersits neighboring subcarriers are now non-zero (indicated by [1]) andinterfere with each other. This should be compared to the strictlyorthogonal conditions in FIG. 2A without ICI.

FIG. 3 is a spectrum diagram which illustrates reducedintercarrier-interferences in a situation where only every othersubcarrier is modulated (solid lines, [1]). The modulated subcarriersare boosted by a value of γ=sqrt(2)≈1.414 to yield unit power, and theunmodulated subcarriers (dashed lines) are shown only for reference andare not actually transmitted. It is easily observed that the largestcontributing interference ([2]) from the two neighboring subcarriers issuppressed, and the CINR at the actively modulated subcarriers ([1]) isincreased.

FIG. 4A shows the relationship of all subcarriers in a situation whereLDM is performed according to FIG. 1 and the compound signal ismodulated onto an OFDM symbol. The upper layer is shown with solidlines, the lower layer after lowering its power to its chosen injectionlevel with dash-dotted lines. FIG. 4B depicts the ICI situation in caseof rapidly time-varying conditions, i.e., ICI is caused by both upperand lower layer.

Hence, in principle, LDM can serve different types of receiver, e.g.mobile and stationary, simultaneously in an information-theoreticallyoptimal way. However, when LDM is paired with OFDM to cope withmultipath effects, a single FFT length is implicitly assigned to bothlayers, although the mobile layer would preferably employ a short FFTfor Doppler resilience and the stationary layer a long FFT for highspectral efficiency.

The present disclosure resolves this conflict between the preference fora long FFT and Doppler resilience with the configuration depicted inFIG. 5.

FIG. 5 is a block diagram which illustrates a technique forconstellation superposition for two-layer LDM according to an embodimentof the present disclosure. FIG. 5 is similar to the generic LDM combinershown in FIG. 1, wherein like elements are identified by like referencenumerals, a detailed description thereof will be omitted.

The configuration of FIG. 5 differs from the conventional configurationof FIG. 1 in that the LDM combiner (100) further comprises anup-sampling unit (60) and a power booster (70) in the upper layerbranch. The up-sampling unit (60) performs M-fold up-sampling on itsinput signal. This may be achieved, for instance, by inserting (M−1)zeros between every two consecutive samples (symbols or cells) of x_(U)at its input, thus yielding the up-sampled signal x_(U) ^(M). Theinsertion of zeroes implies a reduction of power. In order to compensatethe power reduction, a power booster (70) is provided which boosts thesignal's power by a factor γ which equals the square root of theup-sampling factor M, i.e., γ=sqrt(M). This power-boost causes theupper-layer signal γ x_(U) ^(M) to have unit-power.

The benefit of this approach is that the LDM compound signal can becarried on a very long OFDM signal with e.g. 32 k FFT, such that thelower layer can utilize every subcarrier, thus being highly spectralefficient, whereas the upper layer utilizes every M-th subcarrier only,thus being highly robust against Doppler spread.

FIG. 6A is a spectrum diagram which illustrates a transmitted OFDMsymbol with an LDM compound signal according to an embodiment of thepresent disclosure. FIG. 6A is similar to FIG. 4A, except that data ofthe upper layer (solid lines) is modulated on even subcarriers only(M=2), whereas data of the lower layer (dash-dotted lines) is modulatedon all subcarriers. The spectral energy of odd subcarriers of theconventional compound signal of FIG. 4A is represented, for illustrativepurposes only, by dashed lines. This signal component is absent in theLDM compound signal of the present disclosure.

FIG. 6B is a spectrum diagram which illustrates the OFDM symbol of FIG.6A as they are received over a time-varying channel. FIG. 6B is similarto FIG. 4B, except that data of the upper layer (solid lines) ismodulated on even subcarriers only (M=2), whereas data of the lowerlayer (dash-dotted lines) is modulated on all subcarriers. As in FIG.6A, the spectral energy of odd subcarriers of the conventional compoundsignal is represented, for illustrative purposes only, by dashed lines.This signal component is absent in the LDM compound signal of thepresent disclosure. As can be seen from FIG. 6B, and in particular froma comparison of FIGS. 6B and 4B, the inter-carrier interference fromneighboring subcarriers is significantly reduced ([1]), as compared tothe conventional LDM compound signal.

FIG. 7 is a schematic block diagram of a transmitter for two LDM layersaccording to an embodiment of the present disclosure. FIG. 7 is similarto the generic LDM combiner shown in FIG. 1 and the LDM combineraccording to the embodiment of FIG. 5, wherein like elements areidentified by like reference numerals, a detailed description thereofwill be omitted.

The transmitter comprises two BICM units (10, 20) for each of the upperlayer data and the lower layer data, respectively. Each BICM unit (10,20) includes an encoder (not shown) for encoding the input data with anerror correcting code, a bit interleaver (not shown) for increasing theresilience to burst errors, and a cell mapper (not shown) for mappingthe coded and interleaved bit sequence into a base-band sequence ofcomplex digital symbols. The modulated signal of the upper layer and themodulated signal of the lower layer are then combined in LDM combiner(100) into a compound signal, as explained above in conjunction withFIG. 5.

The compound signal generated by the LDM combiner (100) is then fedthrough various other processing units in order to generate the desiredtransmit signal. These processing units may include time interleaver(72), frequency interleaver (74), OFDM framer (80), pilot insertion (notshown), inverse Fourier transformation (not shown), digital/analogconversion (not shown), power amplification (not shown), etc. The resultof these processing steps may then be transmitted by broadcast antennas.

It should be understood that the transmitted signal is provided for twotypes of receivers: (i) a mobile receiver, which experiences highDoppler spread and thus benefits from the virtually increased subcarrierspacing on the upper layer, and (ii) a stationary receiver, which doesnot suffer from high Doppler spread and hence benefits from a long FFTlength.

FIG. 8A is a schematic block diagram for a receiver, e.g., a mobilereceiver, that is configured for receiving the upper layer only. Thereceiver comprises an OFDM demodulator (110) and a frequencydeinterleaver (120) followed by a time deinterleaver (125) for receivinga compound signal. The received compound signal is down-sampled by afactor M in down-sampling unit (130) to isolate the subcarriers thatcarry the upper layer data. The down-sampled signal is then demodulatedin demodulator (140) in order to retrieve the digital data of the upperlayer.

FIG. 8B is a schematic block diagram for a receiver, e.g., a stationaryreceiver, that is configured for receiving both the upper layer and thelower layer. The receiver of FIG. 8B comprises all components of thereceiver of FIG. 8A, including the OFDM demodulator (110), the frequencydeinterleaver (120), and the time interleaver (125) for receiving acompound signal. The received compound signal is down-sampled by afactor M in down-sampling unit (130) to isolate the subcarriers thatcarry the upper layer data. The digital data of the upper layer isretrieved by means of a first demodulator (140).

In order to retrieve also the lower layer data, a modulator 150 isprovided for re-modulating the upper layer data, an up-sampling unit(160) for up-sampling the re-modulated signal, and an amplifier (170)for adjusting the power level of the up-sampled signal. The outputsignal of the amplifier (170) is then subtracted by means of signalsubtractor 180 from the received compound signal, thus providing thereceived compound signal free of the interference from the re-modulatedupper layer signal, which is then demodulated in a second demodulator(190).

The present disclosure has been described in terms of specificembodiments that are not supposed to limit the scope of the appendedclaims. Various modifications can be made without departing from thescope of the appended claims.

For instance, the above embodiments relate to layered divisionmultiplexing with two layers only. The present disclosure, however, canalso be applied to three or more distinct layers. In this case, theup-sampling step may be applied to one or more of the upper-most layers.The upper-most layer may be up-sampled with an up-sampling factor thatis equal to or greater than the up-sampling factor of the next lowerlayer.

Further, a reduction of the inter-carrier interference has beendescribed in conjunction with two-fold up-sampling of the upper layersignal. However, other up-sampling factors, such as M=3 or M=4, etc.,may be employed, depending on data rates, in order to further increasethe spectral distance of subcarriers carrying the upper layer data andto further reduce inter-carrier interference.

Further, the present disclosure has been presented in the context ofdigital data broadcasting based on bit-interleaved coded modulationwhich includes specific forward error correcting codes (FECs), specificbit-interleavers, and specific symbol mappers. However, the presentdisclosure can likewise be applied to any other form of modulation thatconverts digital data into a modulated signal consisting of a sequenceof complex-valued or real-valued cells.

In addition, although description is carried out in the presentdisclosure using the terms up-sampling and down-sampling for the sake ofdescription, up-sampling and down-sampling need not necessarily becarried out. In such a case, processes equivalent to those describedusing the terms up-sampling and down-sampling in the present disclosurecan be performed on the upper layer data and lower layer data usingother arithmetic processing or signal processing, etc.

Finally, although the present disclosure has been presented in thecontext of orthogonal frequency division multiplexing, it may also beapplied to other forms of multi-carrier modulation.

Summarizing, the present disclosure relates a technique for broadcastingdigital data, and in particular to layered-division multiplexing inconnection with orthogonal frequency division multiplexing. In order toreduce inter-carrier interferences for the data of the upper layer whileusing very long OFDM symbols for the data of the lower layer, it is theparticular approach of the present disclosure to up-sample the modulatedupper layer by a factor of M≥2 before combining same with the modulatedlower layer signal. In this manner, upper layer data is modulated onlyon every M-th OFDM subcarrier, thus providing a significant reduction ofICI on time-varying channels.

Embodiment 2

As described in the Background Art section, intuitively, the edge of LDMover TDM/FDM in capacity is obtained due to the simultaneoustransmission of more than one service without pausing in either timedomain or frequency domain. In practice, however, LDM entails higherreceiver complexity as well as constraints in the transmission systemdesign.

A particular constraint of the legacy LDM-system adopted by ATSC 3.0 isthat the upper and lower layer implicitly use the same FFT length.Hence, a compromise must be found for the FFT length, if stationary andmobile receivers are to be served simultaneously. This problem isaddressed by up-sampling (zero-padding) the upper layer—which providesdata to mobile receivers—to affect a larger subcarrier-spacing andthereby increase the robustness against Doppler spread.

Now the following caveat can be observed: After the superposition of theupper and lower layer the compound signal passes through a timeinterleaving stage and a frequency interleaving stage, which have theundesired effect to partially revoke the virtually increasedsubcarrier-spacing of the upper layer. While in principle timeinterleavers, e.g., row-column block interleavers, exist for whichconstant subcarrier spacing could be maintained even after interleaving,this is no longer true for a frequency interleaver which has thecharacteristic of a pseudo-random permutation.

On account of the interleaving the subcarrier spacing of the upper-layerwill no longer be constant, i.e., some subcarriers will be closer toeach other and others will be farther away. As a net effect, what can beobserved is a sub-carrier spacing which is virtually enlarged onaverage. This is to say that the robustness against Doppler becomeshigher with the up-sampling mechanism but applying a conventionalinterleaving technique reduces this robustness to some extent.

In view of the above problems, it is an aim of this embodiment toprovide an improved interleaving structure that can achieve highrobustness against Doppler, in particular in conjunction with anLDM-combiner that employs upper layer up-sampling.

In the context of layered division multiplexing with upper-layerup-sampling, it is the particular approach of the present disclosure toprovide separate interleaving stages for LDM compound cells carryingcells of more than one layer and for LDM compound cells carrying cellsof only one layer. In this manner, time-and frequency interleaving canbe performed on an LDM compound signal while maintaining subcarrierspacing for compound cells carrying cells of more than one layer.

In the following, LDM compound cells carrying cells from more than onelayer will be referred to as superimposed cells whereas LDM compoundcells carrying cells from only one layer will be referred to asnon-superimposed cells.

According to a first aspect of the present disclosure, a method fortransmitting digital data is provided. The method comprises the steps ofgenerating a first modulated signal by modulating digital data of afirst service; generating a second modulated signal by modulatingdigital data of a second service; up-sampling the first modulated signalby inserting (M−1) zeroes between every two consecutive samples of thefirst modulated signal, M being a positive integer greater than 1;generating a compound signal by adding the up-sampled signal and thesecond modulated signal; interleaving the compound signal by applying apermutation to a block of consecutive samples of the compound signal,said permutation being adapted such that a subset consisting of everyM-th sample of the block is mapped onto itself, said subset of everyM-th sample consisting of samples of the compound signal that are thesum of a sample of the first modulated signal and a sample of the secondmodulated signal; and transmitting the interleaved compound signal.

Hence, the interleaving is performed such that the set of superimposedcells, i.e., the subset of samples of the compound signal that are thesum of a sample of the first modulated signal (prior to up-sampling) anda sample of the second modulated signal, is invariant under thepermutation applied. This implies that the complementary set, i.e., theset of non-superimposed cells, is also invariant under the permutationapplied. In other words, superimposed cells are only mapped ontosuperimposed cells, and non-superimposed cells are only mapped ontonon-superimposed cells, or in still other words, superimposed cells andnon-superimposed cells are interleaved independently. In this manner,the subcarrier spacing (i.e., the spectral distance) betweensuperimposed cells is not altered by the interleaving stage.

In an exemplary embodiment, the interleaving step further comprisesdemultiplexing the compound signal into a first sequence of samplesconsisting of every M-th sample of the compound signal and into a secondsequence of samples consisting of the samples of the compound signalthat are not part of the first sequence of samples, the first sequenceof samples consisting of the samples that are the sum of a sample of thefirst modulated signal and a sample of the second modulated signal;applying a first interleaving process to the first sequence of samples;applying a second interleaving process to the second sequence ofsamples; and re-multiplexing the interleaved first sequence of samplesand the interleaved second sequence of samples to obtain the interleavedcompound signal. In this manner, a permutation with the desired propertyof mapping superimposed cells only onto superimposed cells can beimplemented in a straightforward manner.

For example, the first and/or the second interleaving process comprise arow-column interleaving process. Alternatively or additionally, thefirst and/or the second interleaving process comprise a pseudo-randominterleaving process. Pseudo-random and row-column interleaving mayrelate to frequency and time interleaving, respectively.

In an exemplary embodiment, parameters of the first and/or the secondinterleaving process are signaled within an L1-signaling part of arespective data frame. In this manner, interleaving parameters may befreely selected to suit a particular propagation scenario.

An exemplary embodiment further comprises the step of dividing thecompound signal into frames of a predefined length, wherein data of eachframe is transmitted simultaneously by means of orthogonal frequencydivision multiplexing, OFDM. OFDM is the preferred method fortransmitting digital data over a broadband communication channel and isused in many digital broadcasting and communication standards, includingDVB-T2 and ATSC 3.0.

For example, data of the first service is transmitted on every M-th OFDMsubcarrier only. This reduces ICI for the first layer data ontime-varying channels and allows at the same time long OFDM symbols forthe second layer data. Mobile devices may thus receive the first servicewith high reliability, whereas stationary devices may additionallyreceive the second service at a high data rate.

According to a second aspect of the present disclosure, a method forreceiving digital data is provided. Said method comprises the steps ofreceiving a compound signal; demultiplexing a first sequence of samplesfrom the received compound signal, said first sequence of samplesconsisting of every M-th sample of the compound signal, M being apositive integer greater than 1; applying a first de-interleavingprocess to the first sequence of samples; and retrieving digital data ofa first service by demodulating the de-interleaved first sequence ofsamples.

In an exemplary embodiment, the method further comprises the steps ofdemultiplexing a second sequence of samples from the received compoundsignal, said second sequence of samples consisting of samples of thecompound signal that are not part of the first sequence of samples;applying a second de-interleaving process to the second sequence ofsamples; re-multiplexing the de-interleaved first sequence of samplesand the de-interleaved second sequence of samples to obtain ade-interleaved compound signal; generating a re-modulated signal bymodulating the retrieved digital data of the first service; up-samplingthe re-modulated signal by the factor of M; generating a differencesignal by subtracting the up-sampled signal from the deinterleavedcompound signal; and retrieving digital data of a second service bydemodulating the difference signal.

In an exemplary embodiment, the method further comprises the step ofobtaining interleaving parameter information from an L1-signaling fieldin a frame header, wherein at least one of the first de-interleavingprocess and the second de-interleaving process is applied to therespective sequence of samples in accordance with the obtainedinterleaving parameter information. In this manner, interleavingparameters may be freely selected to suit a particular propagationscenario.

In an exemplary embodiment, the compound signal is received by decodinga sequence of OFDM symbols. Moreover, the down-sampling step may keepevery M-th OFDM subcarrier only, thereby achieving a reduction of ICI onrapidly time-varying channels.

According to a third aspect of the present disclosure, a transmitter fortransmitting digital data is provided. The transmitter comprises a firstmodulator for generating a first modulated signal by modulating digitaldata of a first service; a second modulator for generating a secondmodulated signal by modulating digital data of a second service; anup-sampling unit for up-sampling the first modulated signal by inserting(M−1) zeroes between every two consecutive samples of the firstmodulated signal, M being a positive integer greater than 1; a signalcombiner for generating a compound signal by adding the up-sampledsignal and the second modulated signal; an interleaver for interleavingthe compound signal by applying a permutation to a block of consecutivesamples of the compound signal, said permutation being adapted such thata subset consisting of every M-th sample of the block is mapped ontoitself, said subset of every M-th sample consisting of samples of thecompound signal that are the sum of a sample of the first modulatedsignal and a sample of the second modulated signal; and an output stagefor transmitting the compound signal.

According to a fourth aspect of the present disclosure, a receiver forreceiving digital data is provided. The receiver comprises an inputstage for receiving a compound signal; a demultiplexer fordemultiplexing a first sequence of samples from the received compoundsignal, said first sequence of samples consisting of every M-th sampleof the compound signal, M being a positive integer greater than 1; afirst de-interleaver for applying a first de-interleaving process to thefirst sequence of samples; and a first demodulator for retrievingdigital data of a first service by demodulating the de-interleaved firstsequence of samples.

In an exemplary embodiment, the demultiplexer is further adapted fordemultiplexing a second sequence of samples from the received compoundsignal, said second sequence of samples consisting of samples of thecompound signal that are not part of the first sequence of samples.Moreover, the receiver further comprises a second interleaver forapplying a second de-interleaving process to the second sequence ofsamples; a multiplexer for re-multiplexing the de-interleaved firstsequence of samples and the de-interleaved second sequence of samples toobtain a de-interleaved compound signal; a modulator for generating are-modulated signal by modulating the retrieved digital data of thefirst service; an up-sampling unit for up-sampling the re-modulatedsignal by the factor of M; a signal subtractor for generating adifference signal by subtracting the up-sampled signal from thede-interleaved compound signal; and a second demodulator for retrievingdigital data of a second service by demodulating the difference signal.

As described in Embodiment 1, in principle, LDM can serve differenttypes of receiver, e.g. mobile and stationary, simultaneously in aninformation-theoretically optimal way. However, when LDM is paired withOFDM to cope with multipath effects, a single FFT length is implicitlyassigned to both layers, although the mobile layer would preferablyemploy a short FFT for Doppler resilience and the stationary layer along FFT for high spectral efficiency.

Up-sampling the upper layer to increase its subcarrier spacing isproposed. However, interleaving in time and frequency is employedconventionally before OFDM modulation, which partially revokes theincreased subcarrier spacing of the upper layer. In the following, aninterleaving stage will be disclosed that is specifically adapted to theLDM combiner with upper-layer up-sampling in order to maintain (aconstantly increased) subcarrier spacing of superimposed cells on theupper layer.

FIG. 9 is a block diagram which illustrates a technique forconstellation superposition and interleaving for two-layer LDM accordingto an embodiment of the present disclosure. The configuration of FIG. 9resolves the conflict between long FFT length and Doppler resilience andprovides interleaving in time and frequency, such that constantsubcarrier spacing is maintained. The solution consists of two maincomponents, the LDM combiner, which is a modified version of the genericLDM combiner shown in FIG. 1, and the interleaving stage. It should benoted that, OFDM framer 300 is the same as OFDM 80 in Embodiment 1.

The configuration of FIG. 9 comprises two BICM units (10, 11) for eachof the upper layer data and the lower layer data, respectively. EachBICM unit (10, 11) includes an encoder (not shown) for encoding theinput data with an error correcting code, a bit interleaver (not shown)for increasing the resilience to burst errors, and a cell mapper (notshown) for mapping the coded and interleaved bit sequence into abase-band sequence of complex digital symbols. The modulated signal ofthe upper layer and the modulated signal of the lower layer are thencombined in LDM combiner (100) into a compound signal.

The LDM combiner (100) of FIG. 9 is similar to the generic LDM combinershown in FIG. 1, wherein like elements are identified by like referencenumerals, a detailed description thereof will be omitted. Theconfiguration of the LDM combiner (100) of FIG. 9 differs from thegeneric LDM combiner of FIG. 1 in that the LDM combiner (100) furthercomprises an up-sampling unit (160) and a power booster (170) in theupper layer branch. The up-sampling unit (160) performs M-foldup-sampling on its input signal, which is achieved by inserting (M−1)zeros between every two consecutive samples x_(U) at its input, thusyielding the up-sampled signal x_(U) ^(M). The insertion of zeroesimplies a reduction of power. In order to compensate the powerreduction, a power booster (170) is provided which boosts the signal'spower by a factor γ which equals the square root of the up-samplingfactor M, i.e., γ=sqrt(M). This power-boost causes the upper-layersignal γ x_(U) ^(M) to have unit-power.

The benefit of this approach is that the LDM compound signal can becarried on a very long OFDM signal with e.g. 32 k FFT, such that thelower layer can utilize every subcarrier, thus being highly spectralefficient, whereas the upper layer utilizes every M-th subcarrier only,thus being highly robust against Doppler spread. It should be understoodthat the transmitted signal is provided for two types of receivers: i) astationary receiver, which does not suffer from high Doppler spread andhence benefits from a long FFT length, and ii) a mobile receiver, whichexperiences high Doppler spread and thus benefits from the virtuallyincreased subcarrier spacing on the upper layer.

The LDM combiner (100) is followed by an interleaver stage (200), whichis specifically adapted for preserving the spectral distance betweensuperimposed cells. To this end, the interleaving stage (200) comprisestwo branches, namely a first branch (the upper branch in FIG. 9) forprocessing superimposed cells and a second branch (the lower branch inFIG. 9) for processing non-superimposed cells. A demultiplexer, whichmay be implemented as a uniform M-fold down-sampling unit (210) and anon-uniform periodic M-fold down-sampling unit (211), extracts everyM-th cell from the output of the LDM combiner for the first branch andevery other cell for the second branch. Each output branch of thedemultiplexer (down-sampling unit (210, 211)) has both a dedicated timeinterleaver (220, 221) and a dedicated frequency interleaver (230, 231)for interleaving the respective sequence of superimposed andnon-superimposed cells independently of each other in time and frequencydirection.

The interleaving units (i.e., time interleaver (220, 221) and frequencyinterleaver (230, 231)) in FIG. 9 may be implemented independently ofeach other and may operate on different blocks (or “chunks”) of cells.Specifically, the time interleaving units 220 and 221 may be configuredfor applying a first kind of interleaving, such as row-columninterleaving, whereas the frequency interleaving units may be configuredfor applying a different, second kind of interleaving, such aspseudo-random interleaving, or vice versa. Further, each interleavingunit may operate on blocks with block size different from the block sizeof another interleaving unit. This difference may relate to time andfrequency interleaving, as well as to the upper and the lower layer. Thelower layer may, for instance, comprise a row-column interleaver withmore columns and/or rows than a row-column interleaver of the upperlayer, and vice versa. On the other hand, the frequency interleaver ofthe upper layer may operate on a block of cells that is smaller than theblock of cells on which the corresponding time interleaver is operating,or vice versa. The same holds true for the time and frequencyinterleaver of the lower layer. Additional details of the time andfrequency interleavers will be discussed below.

Further, in the embodiment of FIG. 9 there are two independentinterleaving units in each of the upper and the lower branch. However,depending on circumstances, more (e.g. three or four or more independentinterleaving units) or less (e.g. only a single interleaving unit) maybe implemented in either the upper, the lower or in both branches.

Further, the configuration of the interleaving stages in each of theupper branch and the lower branch may be dynamically varied, e.g.,depending on the propagation scenario, the channel properties or thedata to be transmitted, including bit error rate, number of PLPs, numberof LDM layers, QoS requirements, modulation, data rate, etc.Specifically, characteristic parameters of the frequency and/or timeinterleavers such as number of columns/rows of a row-column interleaverand the length of pseudo-random interleaver may be adapted. Parameterscharacterizing the interleaving carried out may then be signaled to thereceiver, as will be discussed below.

Referring back to FIG. 9, both the upper and the lower branches aremerged again by means of a multiplexer, generating the interleavedcompound signal that forms the output of the interleaving stage. Themultiplexer may be implemented as a uniform M-fold up-sampling unit(240) and a non-uniform periodic M-fold up-sampling unit (241) incombination with a signal adder (250) for adding the two up-sampledsignals with the appropriate phase relationship. The operation of theuniform M-fold up-sampling unit (240) may be basically identical to thatof up-sampling unit (160) of the LDM combiner. Other implementations forthe demultiplexer and the multiplexer are conceivable, including clockedswitches and buffers.

FIG. 10A is a spectrum diagram which illustrates a transmitted OFDMsymbol with an LDM compound signal according to an embodiment of thepresent disclosure. FIG. 10A is similar to FIG. 4A, except that data ofthe upper layer (solid lines) is modulated on even subcarriers only(M=2), whereas data of the lower layer (dash-dotted lines) is modulatedon all subcarriers. The spectral energy of odd subcarriers of theconventional compound signal of FIG. 4A is represented, for illustrativepurposes only, by dashed lines. This signal component is absent in theLDM compound signal of the present disclosure.

FIG. 10B is a spectrum diagram which illustrates the OFDM symbol of FIG.10A as they are received over a time-varying channel. FIG. 10B issimilar to FIG. 4B, except that data of the upper layer (solid lines) ismodulated on even subcarriers only (M=2), whereas data of the lowerlayer (dash-dotted lines) is modulated on all subcarriers. As in FIG.10A, the spectral energy of odd subcarriers of the conventional compoundsignal is represented, for illustrative purposes only, by dashed lines.This signal component is absent in the LDM compound signal of thepresent disclosure. As can be seen from FIG. 10B, and in particular froma comparison of FIGS. 10B and 4B, the inter-carrier interference fromneighboring subcarriers is significantly reduced ([1]), as compared tothe conventional LDM compound signal.

The operation of the interleaving stage (200) of FIG. 9 explained withreference to FIGS. 11A and 11B.

FIG. 11A is a schematic representation of a sequence of LDM compoundcells output by an LDM combiner with upper-layer up-sampling. Theup-sampling factor M is 3, hence, every third subcarrier carries cellsfrom both upper and lower layer (superimposed cells marked by an “A”)and all remaining subcarriers carry cells from only the lower layer(non-superimposed cells marked by “B” and “C”).

FIG. 11B is a schematic representation of the interleaving stageoperating on the cell sequence of FIG. 11A. The main purpose of theinterleaving stage is to partition superimposed cells (marked “A”) andnon-superimposed (marked “B” and “C”) into two separate streams ofcells, to interleave these two cell streams independently, and to mergethe two interleaved streams into a single cell stream which is thenpassed on to the framing and OFDM blocks.

In the following, the particular embodiment shown in FIG. 11B isdescribed which allows the realization of this concept.

The interleaving stage in FIG. 11B is receiving the cell sequence ABCABCetc. from the LDM combiner. The cells in the upper branch are passedthrough a uniform M-fold down-sampler (this is the dual operation to theM-fold up sampler in the LDM combiner) which retains every M-th cellsand presents only superimposed cells (marked “A”) at its output. Thosecells are then time-interleaved and frequency-interleaved; the timeinterleaver π_(U) ^(TI) and frequency interleaver π_(U) ^(FI) arespecific to the upper branch and not necessarily the same as theircounterpart in the lower branch. The interleaved cells are then againup-sampled uniformly by a factor M.

The cells on the lower branch are passed through a non-uniform, butperiodic M-fold down sampler (shown as the block

M) which suppresses every M-th cell and presents the cell sequence“BCBC” etc. at its output. It should be emphasized that the uniformdown-sampler keeps every M-th sample, while the non-uniform periodicdown-sampler suppresses every M-th sample. The data rate at the outputof the non-uniform periodic down-sampler is thus reduced by a factor ofM/(M−1).

Next the cells are time-interleaved and frequency-interleaved; the timeinterleaver π_(L) ^(TI) and frequency interleaver π_(L) ^(FI) arespecific to the lower branch and not necessarily the same as theircounterparts in the lower branch. The interleaved cells in the lowerbranch are then again periodically and non-uniformly up-sampled by afactor M and an offset of one sample to position non-zero cells overzeros in-between the two branches. This is taken care of by the blockmarked with the double up-arrow (

M) which inserts a zero between every (M−1) cells.

Examples for particular time interleavers and frequency interleaver canbe found in ETSI EN 302 755, “Digital Video Broadcasting (DVB); Framestructure channel coding and modulation for a second generation digitalterrestrial television broadcasting system (DVB-T2)”, v1.4.1, February2015, e.g., row-column block time interleavers and even-odd frequencyinterleavers and variations thereof for FFT-length up to 2¹⁵=32Ksubcarriers.

As a final step of the interleaving stage, the two branches aresuperimposed once again. Unlike the first superposition in the LDMcombiner, here every non-zero cell from every layer meets with a zerofrom the respective other layer.

The operation of the interleaving stage is thus equivalent to applying apermutation to a block of compound cells such that the subset ofsuperimposed cells ‘A’ is mapped onto itself. In other words, eachsuperimposed cell is mapped to a position of another superimposed cell.Non-superimposed cells ‘B’ and ‘C’ are mapped to arbitrary positionsin-between the superimposed cells. Interleaving in this manner preservesthe spectral distance between superimposed cells.

LDM has been discussed in terms of a single PLP on the upper and thelower layer. In the following, the general case of multiple PLPs on bothlayers in connection with LDM will be considered in conjunction withFIGS. 12A-12E.

In ATSC 3.0, a concept called time interleaver group (TI-group) wasintroduced to handle this general case. A TI-group is represented by acore layer PLP and it consists of a core layer PLP and all enhancedlayer PLPs which are layered-division multiplexed with the core layerPLP. A TI-group identifier is implicitly given by the position of thecore layer PLP in the control signaling.

The L1-signaling in ATSC 3.0 provides a receiver with a PLP's startaddress, the number of cells allocated to the PLP in a frame, and itslocation on either the core or the enhanced layer. Hence, a receiver isrequired to derive itself to which TI-group it belongs potentially bylining up the points of time covered by a PLP and then relate itselfwhich enhanced PLP belongs to which core layer PLP in order to performSIC for detection.

Here, the target is to define a generic form of L1-signaling to uniquelyand explicitly inform the receiver about the chosen LDM andinterleaving-parameters. To this end, the definition of an LDM-group isintroduced as a group of PLPs consisting of a single core layer PLP andone or more enhanced PLPs, which are layered-division multiplexed withthe core layer PLP. The idea is to associate a PLP with a particularLDM-group identifier and then use the LDM-group identifier to subsumeall LDM-and interleaving parameters in a single unique place within thecontrol signaling.

Before describing a particular solution for the L-signaling it isinstructive to understand that the presence of multiple PLPs on bothlayers may lead to a variety of different alignments of the FEC-blockscontained in an LDM-group. Five FEC-blocks alignments are discussed nextto illustrate the concept from the most simple to the most complex.

In FIG. 12A, the simplest configuration appears, in which one core PLPand one enhanced PLP form a single LDM-group. In addition, the PLPs arecompletely overlapping. There are two underlying assumptions, here: 1)The core layer (plp_id_0) and the enhanced layer carry a certain numberof FEC-blocks, which—depending on the modulation order—are notnecessarily the same. 2) The core layer is presented already in itsstate after M-fold up-sampling.

In FIG. 12B, an additional PLP (plp_id_2) joins the pair. One core PLP(plp_id_0) and one enhanced PLP (plp_id_1) form a first LDM-group(ldm_group_0) and a single PLP (plp_id_2) on the core layer forms asecond LDM-group (ldm_group_1).

The following configurations differ from the former two by introducingPLPs which are overlapping while residing on different LDM-layers. InFIG. 12C, three PLPs are present on the core layer and a single PLP onthe enhanced layer. Following the rationale of ATSC 3.0, the core layerdetermines the interleaving and the affected PLP on the enhanced layerfollows suit. Hence, the core layer splits the enhanced layer into threeLDM-groups (ldm_group_0, ldm_group_1, ldm_group_2).

The reverse situation occurs in FIG. 12D, where a single PLP (plp_id_0)is present on the core layer and extends over three PLPs (plp_id_1,plp_id_2, and plp_id_3) on the enhanced layer. In contrast to theprevious case, but again following the rationale of ATSC 3.0, a singleLDM-group (ldm_group_0) is formed.

The most complex case is depicted in FIG. 12E. There are four PLPs intotal, two on each the core and the enhanced layer, however, the fourthPLP (plp_id_3) overlaps with two core PLPs plp_id_0 and plp_id_1. Itthus is split between two LDM groups, ldm_group_0 and ldm_group_1. Thenumber of FEC-blocks falling into each core layer PLP is signaled asplp_fec_blocks_in_ldm_groups, and the number of core layers to which anenhanced layer PLP belongs is signaled as num_plp_in_ldm_groups.

An exemplary embodiment for the time interleaving is row-column blockinterleaving as employed in DVB-T2. Choice and design of thetime-interleavers will be discussed using the following nomenclature:

N_(cells) ^(u) Number of cells per FEC-block for the upper layerN_(FEC_TI) ^(u) Number of FEC-blocks per TI-Block on the upper layerN_(cells) ^(l)(i) Number of cells per FEC-block for the lower layer andthe i-th PLPN_(FEC_TI) ^(l)(i) Number of FEC-blocks per TI-Block on the lower layerand the i-th PLP

An essential constraint is the following:

$\begin{matrix}{{M \cdot N_{cells}^{u} \cdot N_{FEC\_ TI}^{u}} = {\sum\limits_{i}{{N_{cells}^{l}(i)} \cdot {N_{FEC\_ TI}^{l}(i)}}}} & (1)\end{matrix}$

meaning that within an LDM-group the number of cells on the upper layerafter up-sampling (on the left hand side) must equal the number of cellson the lower layer (on the right hand side). The sum takes into accountthose FEC-block alignments in which a core layer PLP extends overmultiple enhanced layer PLPs (cf. FIGS. 12D and 12E).

The number of cells entering the time-interleaver π_(U) ^(TI) on theupper branch is

N _(cells) ^(u) ·N _(FEC_TI) ^(u)

which is an integer and a block-interleaver is easily realized. No issuethere. However, the number of cells for the time-interleaver π_(L) ^(TI)on the lower branch is

${N_{cells}^{u} \cdot {N_{FEC\_ TI}^{u}\left( {M - 1} \right)}} = {\left( {1 - \frac{1}{M}} \right){\sum\limits_{i}{{N_{cells}^{l}(i)} \cdot {N_{FEC\_ TI}^{l}(i)}}}}$

with M being the up-sampling factor.

Conceptually, the down-sampling on the lower branch is best thought ofas a puncturing process, i.e., before time-interleaving a FEC-block isactually shortened from a FEC-block with N_(cells) ^(l)(i) cells to aFEC-block with

${N_{cells}^{l}(i)} \cdot \left( {1 - \frac{1}{M}} \right)$

cells.

FIGS. 13A and 13B illustrate the layout for the time interleavers π_(U)^(TI) and π_(L) ^(TI) (for a single PLP on the lower layer),respectively, in accordance with the above considerations.

The term

$\left( {1 - \frac{1}{M}} \right)$

is potentially troublesome as it may yield a non-integer number.Fortunately, for long FEC-codes with 64800 code bits this is not thecase since the puncturing yields an integer number of samples for allQAM-constellations up to 4096-QAM and up to down-sampling factors M=6.However, for short FEC codes with 16200 code bits, cases exists, inwhich a non-integer number of samples arises, i.e.,

-   -   256QAM and M=2,    -   16QAM and M=4,    -   256QAM and M=4,    -   256QAM and M=6.

Since the enhanced/lower layer usually carries high-rate services withlong LDPC codeword's, these can be considered corner cases. A possiblesolution, which also covers these corner cases, is to combine a coupleof FEC-blocks to form a super-FEC-block before passing them through theinterleaver. Conceptually, this is achieved by allowing thetime-interleaver to have a variable number of rows in addition to avariable number of columns.

The same approach of allowing a time-interleaver layout with completelyvariable number of columns and rows also facilitates the situation inwhich there are multiple enhanced PLPs per core layer PLP present. Thetime-interleaver layout in FIG. 13 reflects a one-on-one FEC-blockalignment as, e.g., in FIG. 12A. Here, the choice of rows and columnsfor the TI is straightforward. The situation is different if there aremultiple enhanced PLPs present as, e.g., in FIGS. 12D and 12E. Forsimplicity, we assume two PLPs on the enhanced layer. They areillustrated in FIGS. 14A and 14B.

The two PLPs are jointly passed into a time-interleaver whose dimensionsare generically signaled with num_ti_rows_lower andnum_ti_columns_lower, cf. FIG. 14C).

An exemplary embodiment for the frequency interleaving (FI) is thepseudo-random solution as employed in DVB-T2. According to DVB-T2, theparameters of the FI (such as sequence length for the frequencyinterleaver and the number data cells in an OFDM cell) are chosenimplicitly based on the chosen FFT-length and pilot pattern. The FI inDVB-T2 is conceptually a part of the OFDM-modulation and applies to allsubcarriers, not individual PLPs.

According to ETSI EN 302 755 v1.4.1, the permutation function H(p) forDVB-T2 is determined by the algorithm:

p = 0; for  (i = 0; i < M_(max); i = i + 1)$\left\{ {{{H(p)} = {{\left( {i\mspace{14mu} {mod}\mspace{11mu} 2} \right){.2}^{N_{r} - 1}} + {\sum\limits_{j = 0}^{N_{r} - 2}{{R_{i}(j)}{.2}^{j}}}}};{{{if}\mspace{14mu} \left( {{H(p)} < N_{data}} \right)p} = {p + 1}};} \right\}$

FFT Size M_(max) 1K 1 024 2K 2 048 4K 4 096 8K 8 192 16K  16 384  32K 32 768 

A frequency interleaver can span up to N_(data)<=M_(max) cells. Thetime-interleaver will usually span more than N_(data) cells, say Kcells, i.e., K>=N_(data). The integer K can assume the value N_(cells)^(u)·N_(FEC_TI) ^(u) for the upper interleaving branch and

${N_{cells}^{u} \cdot {N_{FEC\_ TI}^{u}\left( {M - 1} \right)}} = {\left( {1 - \frac{1}{M}} \right){\sum\limits_{i}{{N_{cells}^{l}(i)} \cdot {N_{FEC\_ TI}^{l}(i)}}}}$

for the lower interleaving branch. An example is shown in FIG. 15.

The frequency interleaver will generally be applied to multiple blocksof cells at the time-interleaver output. There are floor(K/N_(data))blocks containing N_(data) cells, followed by zero blocks or onetrailing block containing K % N_(data) cells. It is understood that inthe presence of a trailing block, which contains K % N_(data) cells, theif-clause in the above algorithm, namely if (H(p)<N_(data)) is changedto if (H(p)<K % N_(data)).

In contrast to DVB-T2, where the frequency interleaver applies to allsubcarriers, in the present disclosure, the FI becomes part of anLDM-group and is thus signaled in the L1 configurable/L1-basic part asnum_mode_fi_upper and num_fi_mode_lower, thereby representing M_(max)for each interleaving branch. Since N_(data) can be chosen independentlyfrom the FFT-length, it is also signaled as part of the dynamicL1-signalling as num_fi_data_upper and num_fi_data_lower for the upperand lower interleaving branch, respectively.

Data is usually transmitted in frames which are partitioned into apreamble part and a payload part. The preamble carries so-calledL1-signaling and consists of parameters, which are required by receiversto be able to demodulate the data carried in the payload. Examples ofsuch parameters may be the employed FEC-code or modulation for a PLP.

Usually L1-signalling is divided into those parameters which areconstant for several frames and those which are more dynamicallychanging, possibly between frames. In DVB-T2, L1-signalling is dividedinto L1-pre and L1-post, whereby the latter is again divided into aconfigurable and a dynamic part. And in ATSC 3.0, similarly,L1-signalling is carried in a basic and a dynamic part.

Potential configurable L1-signalling for the present disclosure is shownin Table 1. The number of PLPs is denoted by num_plp. The type of layer(core/upper or enhanced/lower) is denoted by plp_layer. An identifiercalled ldm_group_id is introduced to uniquely link PLPs on the lowerlayer to the respective upper layer PLP.

As an aside on time-interleaving modes it is noted that, in DVB-T2,there is the concept of intra-frame and inter-frame time-interleaving.Intra-frame time-interleaving allows to time-interleave multipleso-called TI-blocks (one TI-block comprises multiple FEC-blocks andcorresponds to the one-time usage of the time-interleaver) within asingle T2-frame, whereas inter-frame time-interleaving corresponds tothe interleaving of a single TI-block over multiple TI-frames.Furthermore, in DVB-T2, the type of time interleaving (intra-frame orinter-frame interleaving) is signaled by the flag time_il_type and thenumber of TI-blocks is given by time_il_length.

In principle, the concept of intra/inter-frame interleaving is alsoapplicable to LDM, which means that a core layer PLP determines thetime-interleaving mode. This is hence signaled by the flags time_il_typeand time_il_length in Table 1. One constraint must be adhered to incases with overlapping PLPs as in FIG. 12E. Here, all core layer PLPswhich carry parts of an enhanced layer PLP should employ the sametime-interleaving mode. These constraints are, however, outside of thescope of this disclosure and must be arranged by a respectivespecification.

In case that there are multiple core PLPs per enhanced layer PLP, thenumber of core PLPs is signaled as num_plp_ldm_groups, followed by alist of LDM-group identifiers (ldm_group_id) signifying to which corelayer PLPs the enhanced PLP is connected.

The total number of LDM-groups is denoted as num_ldm_groups. It isidentical to the number of core layer PLPs. For each LDM-group, theup-sampling factor is signaled as plp_up_sampling_factor, the boostfactor as plp_boost_factor, the injection level as plp_injection_level,and the maximum number of FEC-Blocks on the upper and lower layer asnum_ti_columns_upper_max and num_ti_columns_lower_max, respectively.

TABLE 1 L1-signalling as part of L1-post configurable or L1-Basic Syntax... num_plp ... for i = 0 .. num_plp−1 {   ...   plp_layer   if(plp_layer == 0) {     ...     ldm_group_id     time_il_type    time_il_length   ...   } else {     num_plp_in_ldm_groups     for i= 0 .. num_plp_in_ldm_groups−1 {       ldm_group_id     }   }   ... }... num_ldm_groups for ldm_group_id = 0 .. num_ldm_groups −1 {  plp_up_sampling_factor   plp_boost_factor   plp_injection_level  num_ti_columns_upper_max   num_ti_columns_lower_max  num_fi_mode_upper   num_fi_mode_lower }   ...

With reference to the constraint in Eq. (1), the number of FEC-blocks,N_(FEC_TI) ^(u) and N_(FEC_TI) ^(l) are signaled as part of the dynamicL1-signalling (see Table 2). Since it is possible for an enhanced PLP topartake in multiple core layer PLPs, the number of FEC-blocksoverlapping with each core layer PLP is signaled asplp_fec_blocks_in_ldm_group.

Additionally, for each LDM-group the LDM-group identifier ldm-group_idis signaled followed by the specific layout of the time-interleavers,π_(U) ^(TI) and π_(L) ^(TI), i.e., their number of columns(num_ti_columns_upper, num_ti_columns_lower) and number of rows(num_ti_rows_upper, num_ti_rows_lower).

Finally, num_fi_mode_upper and num_fi_mode_lower signal the frequencyinterleaver mode (M_(max)) for the upper and lower layer.

Hence, a set of parameters that identify the particular LDMconfiguration may be signaled together with a set of parameters thatidentify the particular interleaver configuration. Both parameter setsmay be logically linked by a common identifier, such as ldm_group_id.Other means for logical grouping or linking may be employed.

Tables 1 and 2 show an example embodiment for signaling both LDM-andinterleaver-related parameters. However, the present disclosure is notlimited to this particular embodiment and a different syntax may beemployed, depending on circumstances. The syntax may, for instance,include additional parameters, exclude some of these parameters, orprovide these parameters in an alternative order or logical grouping.

TABLE 2 L1-signalling as part of L1-post dynamic or L1-Detail Syntax ...for i = 0 .. num_plp−1 {   ...   plp_id   plp_start   if (plp_layer ==0) {     plp_num_blocks   } else {     for i = 0 ..num_plp_in_ldm_groups−1 {       plp_fec_blocks_in_ldm_group     }   }  ... } ... for i = 0 .. num_ldm_groups −1 {   ldm_group_id  num_ti_columns_upper   num_ti_rows_upper   num_ti_columns_lower  num_ti_rows_lower   num_fi_data_upper   num_fi_data_lower }

FIG. 16A is a schematic block diagram for a receiver, e.g., a mobilereceiver that is configured for receiving the upper layer only. Thereceiver comprises an OFDM demodulator (300′) for receiving a compoundsignal. The received compound signal is down-sampled by a factor M indown-sampling unit (210) to isolate the subcarriers that carry the upperlayer data. The down-sampled signal is then deinterleaved in frequencydeinterleaver (220′) and time deinterleaver (230′) and demodulated indemodulator (10′) in order to retrieve the digital data of the upperlayer. Frequency deinterleaver (220′) and time deinterleaver (230′)perform the inverse operation of frequency interleaver (220) and timeinterleaver (230), respectively, described in conjunction with FIGS. 9and 11, e.g., by applying a permutation that is the inverse of thepermutation applied by the respective interleaver. Information onparameters that characterize the permutations to be applied may be takenfrom signaling information such as the L1-signaling described above.

FIG. 16B is a schematic block diagram for a receiver, e.g., a stationaryreceiver that is configured for receiving both the upper layer and thelower layer. The receiver of FIG. 16B comprises all components of thereceiver of FIG. 16A, including the OFDM demodulator (300′), thedown-sampling unit (210), the frequency and time interleavers (220′,230′) and the demodulator (10′) for retrieving the digital data of theupper layer.

The receiver of FIG. 16B is further provided with a branch fordeinterleaving non-superimposed cells. To this end, cells of thereceived signal are effectively demultiplexed into superimposed cellsand non-superimposed cells by means of down-sampling units 210 and 211,respectively. The superimposed cells are deinterleaved in the upperbranch of FIG. 12B as described in conjunction with FIG. 12A. Thenon-superimposed cells are deinterleaved by means of frequencydeinterleaver (221′) and time deinterleaver (231′) which perform theinverse operation of frequency interleaver (221) and time interleaver(231), respectively, described in conjunction with FIGS. 9 and 11, e.g.,by applying a permutation that is the inverse of the permutation appliedby the respective interleaver. The deinterleaved cells of both branchesare then re-multiplexed by means of two up-sampling units (240, 241) anda signal adder (250), as described above. The output of the signal adder(250) is the deinterleaved compound signal as it is received by thereceiver.

In order to extract the lower layer data from the deinterleaved compoundsignal, a modulator (10) is provided for re-modulating the upper layerdata, an up-sampling unit (160) for up-sampling the re-modulated signal,and an amplifier (170) for adjusting the power level of the up-sampledsignal. The output signal of the amplifier (170) is then subtracted bymeans of signal subtractor (140′) from the deinterleaved compoundsignal, thus providing the received compound signal free of theinterference from the re-modulated upper layer signal, which is thendemodulated in a second demodulator (11′).

The present disclosure has been described in terms of specificembodiments that are not supposed to limit the scope of the appendedclaims. Various modifications can be made without departing from thescope of the appended claims.

For instance, the above embodiments relate to layered divisionmultiplexing with two layers only. The present disclosure, however, canalso be applied to three or more distinct layers. In this case, theup-sampling step may be applied to one or more of the upper-most layers.Cells of the respective layers may be subjected to dedicatedinterleavers by demultiplexing and re-multiplexing the compound signalaccordingly. The upper-most layer may be up-sampled with an up-samplingfactor that is equal to or greater than the up-sampling factor of thenext lower layer.

Further, a reduction of the inter-carrier interference has beendescribed in conjunction with two-fold up-sampling of the upper layersignal. The interleaving and deinterleaving stages have been describedin conjunction with a three-fold up-sampling of the upper layer signal.However, any suitable up-sampling factor, such as M=2, M=3 or M=4, etc.,may be employed, depending on data rates, in order to further increasethe spectral distance of subcarriers carrying the upper layer data andto further reduce inter-carrier interference.

Further, the present disclosure has been presented in the context ofdigital data broadcasting based on bit-interleaved coded modulationwhich includes specific forward error correcting codes (FECs), specificbit-interleavers, and specific symbol mappers. However, the presentdisclosure can likewise be applied to any other form of modulation thatconverts digital data into a modulated signal consisting of a sequenceof complex-valued or real-valued cells.

Finally, although the present disclosure has been presented in thecontext of orthogonal frequency division multiplexing, it may also beapplied to other forms of multi-carrier modulation.

Summarizing, the present disclosure relates to a technique forbroadcasting digital data, and in particular to layered-divisionmultiplexing (LDM) in connection with orthogonal frequency divisionmultiplexing, wherein the upper layer data is modulated only on everyM-th OFDM subcarrier in order to reduce inter-carrier interferences. Thedisclosure provides separate interleaving stages for LDM compound cellscarrying cells of more than one layer and for LDM compound cellscarrying cells of only one layer. In this manner, time-and frequencyinterleaving can be performed on an LDM compound signal whilemaintaining subcarrier spacing for compound cells carrying cells of morethan one layer.

It should be noted that the transmitters in each of the foregoingembodiments can be also be represented as indicated below.

FIG. 17 is a block diagram illustrating a configuration of transmitter500.

As illustrated in FIG. 17, transmitter 500 includes mapper 510 andframer 520.

Transmitter 500 transmits a first data sequence and a second datasequence by orthogonal frequency division multiplexing (OFDM).

Mapper 510 obtains the first data sequence and the second data sequence,and combines and maps the first data sequence and the second datasequence obtained onto a plurality of subcarriers which are OFDMsubcarriers. Furthermore, the mapper 510: (a) maps data included in thefirst data sequence and data included in the second data sequence onto aplurality of first subcarriers out of the plurality of subcarriers; and(b) maps the data included in the second data sequence, out of the dataincluded in the first data sequence and the data included in the seconddata sequence, onto a plurality of second subcarriers different from theplurality of first subcarriers, out of the plurality of subcarriers.

Framer 520 generates an OFDM signal from the plurality of subcarriers.

Accordingly, transmitter 500 is capable of improving digital datatransmission performance.

FIG. 18 is a block diagram illustrating a configuration of receiver 600.

As illustrated in FIG. 18, receiver 600 includes receiving device 610and retriever 620.

Receiver 600 receives a first data sequence and a second data sequenceby orthogonal frequency division multiplexing (OFDM).

Receiving device 610 receives an OFDM signal.

Retriever 620 retrieves the first data sequence and the second datasequence from the OFDM signal received by receiving device 610.Furthermore, retriever 620: (a) retrieves data included in the firstdata sequence and data included in the second data sequence, from aplurality of first subcarriers out of a plurality of subcarriers whichare OFDM subcarriers; and (b) retrieves the data included in the seconddata sequence out of the data included in the first data sequence andthe data included in the second data sequence, from a plurality ofsecond subcarriers different from the first subcarriers, out of theplurality of subcarriers.

Accordingly, receiver 600 is capable of improving digital data receivingperformance.

FIG. 19 is a flowchart illustrating the transmitting method according tothe respective embodiments. This method is a method of transmitting afirst data sequence and a second data sequence by orthogonal frequencydivision multiplexing (OFDM).

In step S510, the transmitter obtains the first data sequence and thesecond data sequence, and combines and maps the first data sequence andthe second data sequence obtained onto a plurality of subcarriers whichare OFDM subcarriers. In the mapping: (a) data included in the firstdata sequence and data included in the second data sequence are mappedonto a plurality of first subcarriers out of the plurality ofsubcarriers; and (b) the data included in the second data sequence, outof the data included in the first data sequence and the data included inthe second data sequence, are mapped onto a plurality of secondsubcarriers different from the plurality of first subcarriers, out ofthe plurality of subcarriers.

In step S520, an OFDM signal is generated from the plurality ofsubcarriers.

Accordingly, digital transmission performance can be improved.

FIG. 20 is a flowchart illustrating the receiving method according tothe respective embodiments. This method is a method of receiving a firstdata sequence and a second data sequence by orthogonal frequencydivision multiplexing (OFDM).

In step S610, an OFDM signal is received.

In step S620, the first data sequence and the second data sequence areretrieved from the OFDM signal received by the receiving device. In theretrieving: (a) data included in the first data sequence and dataincluded in the second data sequence are retrieved from a plurality offirst subcarriers out of a plurality of subcarriers which are OFDMcarriers; and (b) the data included in the second data sequence, out ofthe data included in the first data sequence and the data included inthe second data sequence, are retrieved from a plurality of secondsubcarriers different from the first subcarriers, out of a plurality ofsubcarriers.

Accordingly, receiver 600 is capable of improving digital data receivingperformance.

It should be noted that although in each of the foregoing embodiments,the respective structural components are configured using dedicatedhardware, the respective structural components may be implemented byexecuting software programs suitable for the respective structuralcomponents. The respective structural components may be implemented by aprogram executor such as a CPU or a processor reading and executing asoftware program recorded on a recording medium such as a hard disk or asemiconductor memory. Here, the software for realizing the transmitterand receiver, etc. in each of the foregoing embodiments is a programsuch as that described below.

Specifically, the program causes a computer to execute a transmittingmethod of transmitting a first data sequence and a second data sequenceby orthogonal frequency division multiplexing (OFDM), the transmittingmethod including: obtaining the first data sequence and the second datasequence, and combining and mapping the first data sequence and thesecond data sequence obtained onto a plurality of subcarriers which areOFDM subcarriers; and generating an OFDM signal from the plurality ofsubcarriers, wherein in the mapping: (a) data included in the first datasequence and data included in the second data sequence are mapped onto aplurality of first subcarriers out of the plurality of subcarriers; and(b) the data included in the second data sequence, out of the dataincluded in the first data sequence and the data included in the seconddata sequence, are mapped onto a plurality of second subcarriersdifferent from the plurality of first subcarriers, out of the pluralityof subcarriers.

Furthermore, the program causes a computer to execute a receiving methodof receiving a first data sequence and a second data sequence byorthogonal frequency division multiplexing (OFDM), the receiving methodincluding: receiving an OFDM signal; and retrieving the first datasequence and the second data sequence from the OFDM signal that wasreceived, wherein in the retrieving: (a) data included in the first datasequence and data included in the second data sequence are retrievedfrom a plurality of first subcarriers out of a plurality of subcarrierswhich are OFDM carriers; and (b) the data included in the second datasequence, out of the data included in the first data sequence and thedata included in the second data sequence, are retrieved from aplurality of second subcarriers different from the first subcarriers,out of a plurality of subcarriers.

Although transmitters, receivers, etc., according to one or more aspectsare described thus far based on the foregoing embodiments, the presentdisclosure is not limited to the foregoing embodiments. Furthermore,various modifications to the embodiments that may be conceived by aperson of ordinary skill in the art or those forms obtained by combiningstructural components in the different embodiments, for as long as theydo not depart from the essence of the present disclosure, may beincluded in one or more aspects.

What is claimed is:
 1. A transmitter comprising: a mapping circuitconfigured to combine and map a first data sequence and a second datasequence onto orthogonal frequency division multiplexing (OFDM)subcarriers which include first subcarriers and second subcarriers; anda framing circuit configured to generate an OFDM signal from the OFDMsubcarriers, wherein the mapping circuit is configured to: map firstdata included in the first data sequence and second data included in thesecond data sequence onto the first subcarriers; and map the second dataonto the second subcarriers, the first data being not mapped on thesecond subcarriers.
 2. The transmitter according to claim 1, wherein thefirst subcarriers correspond to every n-th subcarrier along a frequencyaxis, n being an integer larger than 1, and the mapping circuit: mapsthe first data onto the first subcarriers as a high power signal; andmaps the second data included onto the first subcarriers and the secondsubcarriers as a low power signal having power lower than power of thehigh power signal.
 3. The transmitter according to claim 2, wherein aratio of the power of the high power signal to the power of the lowpower signal is bigger when n is bigger.
 4. The transmitter according toclaim 1, further comprising: an interleaving circuit configured tointerleave data that are to be mapped onto the OFDM subcarriers, whereinthe interleaving circuit: switches data mapped onto one first subcarrierwith data mapped onto another first subcarrier, the one first subcarrierand the other first subcarrier being included in the first subcarriers;and switches data mapped onto one second subcarrier with data mappedonto another second subcarrier, the one second subcarrier and the othersecond subcarrier being included in the second subcarriers.
 5. Thetransmitter according to claim 4, wherein the interleaving circuitincludes a frequency interleaving circuit, and the frequencyinterleaving circuit: switches the data mapped onto the one firstsubcarrier with the data mapped onto the other first subcarrier, theother first subcarrier being different in frequency from the one firstsubcarrier; and switches the data mapped onto the one second subcarrierwith the data mapped onto the other second subcarrier, the other secondsubcarrier being different in frequency from the one second subcarrier.6. The transmitter according to claim 4, wherein the interleavingcircuit includes a time interleaving circuit, and the time interleavingcircuit: switches the data mapped onto the one first subcarrier with thedata mapped onto the other first subcarrier, the other first subcarrierbeing different from the one first subcarrier in at least one offrequency or time; and switches the data mapped onto the one secondsubcarrier with the data mapped onto the other second subcarrier, theother second subcarrier being different from the one second subcarrierin at least one of frequency or time.
 7. The transmitter according toclaim 1, wherein the mapping circuit comprises an up-sampling circuitconfigured to perform up-sampling on the first data sequence.
 8. Areceiver comprising: an antenna through which an orthogonal frequencydivision multiplexing (OFDM) signal is received; and a retrievingcircuit configured to retrieve at least one of a first data sequence ora second data sequence from the OFDM signal, wherein the retrievingcircuit is configured to: retrieve first data included in the first datasequence and second data included in the second data sequence from firstOFDM subcarriers; and/or retrieve the second data from second OFDMsubcarriers different from the first OFDM subcarriers.
 9. The receiveraccording to claim 8, wherein the first subcarriers correspond to everyn-th subcarrier along a frequency axis, n being an integer larger than1, and the retrieving circuit: retrieves the first data from the firstsubcarriers as a high power signal; and retrieves the second data fromthe first subcarriers and the second subcarriers as a low power signalhaving power lower than power of the high power signal.
 10. The receiveraccording to claim 9, wherein a ratio of the power of the high powersignal to the power of the low power signal is bigger when n is bigger.11. The receiver according to claim 8, further comprising: adeinterleaving circuit configured to switch data mapped onto one firstsubcarrier with data mapped onto another first subcarrier and switchdata mapped onto one second subcarrier with data mapped onto anothersecond subcarrier, in the OFDM signal, the one first subcarrier and theother first subcarrier being included in the first subcarriers, the onesecond subcarrier and the other second subcarrier being included in thesecond subcarriers.
 12. The receiver according to claim 11, wherein thedeinterleaving circuit includes a frequency deinterleaving circuit, andthe frequency deinterleaving circuit: switches the data mapped onto theone first subcarrier with the data mapped onto the other firstsubcarrier, the other first subcarrier being different in frequency fromthe one first subcarrier; and switches the data mapped onto the onesecond subcarrier with the data mapped onto the other second subcarrier,the other second subcarrier being different in frequency from the onesecond subcarrier.
 13. The receiver according to claim 11, wherein thedeinterleaving circuit includes a time deinterleaving circuit, and thetime deinterleaving circuit: switches the data mapped onto the one firstsubcarrier with the data mapped onto the other first subcarrier, theother first subcarrier being different from the one first subcarrier inat least one of frequency or time; and switches the data mapped onto theone second subcarrier with the data mapped onto the other secondsubcarrier, the other second subcarrier being different from the onesecond subcarrier in at least one of frequency or time.
 14. The receiveraccording to claim 8, wherein the retrieving circuit comprises adown-sampling circuit configured to perform down-sampling on the OFDMsignal.
 15. A transmitting method comprising: combining and mapping afirst data sequence and a second data sequence onto orthogonal frequencydivision multiplexing (OFDM) subcarriers which include first subcarriersand second subcarriers; and generating an OFDM signal from the OFDMsubcarriers, wherein first data included in the first data sequence andsecond data included in the second data sequence are mapped onto thefirst subcarriers; and the second data are mapped onto the secondsubcarriers, the first data being not mapped on the second subcarriers.16. A receiving method comprising: receiving an orthogonal frequencydivision multiplexing (OFDM) signal; and retrieving at least one of afirst data sequence or a second data sequence from the OFDM signal,wherein: first data included in the first data sequence and second dataincluded in the second data sequence are retrieved from first OFDMsubcarriers; and/or the second data are retrieved from second OFDMsubcarriers, the first data being not mapped on the second subcarriers.